For starters Ive done a lot of reading and testing different parts. Im at a stand still and I dont want to be a parts changer..I bought a 02 3500 4x4 6 speed cummins 4.10 gears with 270k miles a week ago. All stock except for k&n intake and straight piped. I am experiencing a few problems. I noticed that the heat was barly warm. With a hint of antifreeze smell with blower on and selected on warm. So first problem is heater core. Ive driven the truck around town 55-60 mph. Coolant temp stays around 190 degrees. Once I hit the interstate at 70-75 with the 4.10 gears im turning about 2300-2400 rpm. The coolant temp starts to climb as the speed increase. Upwards of 220+ when im running 80. As soon as I slow back to 65-70 the temps go back to 190-200. Everytime I go to 80 and back down to 65 the temps go up and down every time. Keep in mind that its only around 50 degrees out. Moving on I drove truck for a 1 hr yesterday morning and it was 40 degrees out. temps did same as stated above but When I got home the radiator was cold to the touch and the radiator cap was not under pressure. Upper radiator hose was hot and lower hose was warm/hot. Coolant was full in both radiator and overflow tank. Both heater core hoses were hot. I read a lot about cooling issues and the radiator / intercooler/ conderser are clean from debris, the fan clutch was replaced by previous owner a month ago and has resistance when engine is cold. When spun by hand it only spins freely about a inch. When engine is normal temp 190ish and I cut off motor, the fan stops imediatlly. I first thought fan clutch was bad because temp was increasing with motor speed/vehicle speed. I dont hear it enguaged while the engine is upwards of 220..but i do have stright pipe and turbo sliencer ring is MIA. So its loud already. Second the thermostat could be bad, but cooling does perfect around town as long as im below 60mph. I put water through heater core and it wasnt plugged. Refilled coolant and tried to bleed all air from system. Used allen plug near t-stat. Filled overflow bootle and got engine warm and let it cool down a few times. No coolant was used. both overflow and rad are still both full. Still same symtoms. Oil looks good with no water residue. No exterior coolant leaks. no play or leaking water pump, coolant is nice and green. So either a faulty sensor, plugged radiator, broken water pump impeller, bad thermostat, bad clutch or air in system. Again systoms are semi warm heat with antifreeze smell inside cab. Coolant temp increases with vehicle speed above 70mph and continues to increase until i slow down but is normal around town doing 55-60 even when I accel hard. Sorry for the long story but Any help will be great.

 

Whell lets start here, to me it its sounds like the water pump took a crap you should have pressure on the cap espicially when the truck is warm. But also keep in mind these blocks are thick enough that air alone can keep them somewhat cool, but excessive loads or speeds will no longer keep the engine cool. If you have a coolant system pressure test. You can put it on the cap pump it up to the Manufacture Speced PSI and see if it leaks. If not then bleed the pressure and then start the truck and see if it will build presssure if not then you either have a faulty Thermostat or bad water pump. But if you have a broken impeller or bad bearing you can take the serpentine belt off and grab the water pump and see if their any excessive play or grinding noise. If not then take the thermostat off and put it in 190*-200* water and see if it opens. If not then you have a faulty Thermostat... Replace parts and needed for repair.. If you dont have a way to test the Coolant Systems Pressure you can also still check the WP, and Thermostat without it..

 

I will check those. I did check the water pump and it had a little resistance when spinning and had no play in the bearing. Also the rad cap may be bad too. What is a good way to bleed the air out. I've read many different ways

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I'm gonna say the issue with the smell in the cab is from the heater core. That's the only place coolant is gonna be in contact with a way into the cab. Next thing I would do is pull out the thermostat and put it in water to test it. I just drove home from work for an hour and the engine was at 190 the whole time and my rad cap wasn't hot either. I doubt that's an issue. And when u test your thermostat drain all the coolant out. When you put the coolant back in the rad. Jack up the front passenger side of the truck. This is the best way to remove air from the cooling system without the use of the vaccum pump like a dealership would have. To do some easy checks for the clutch fan, with the engine off spin the fan. You should feel resistance in it. If its spins to freely that's an issue. Another way is to look at the front of the fan hub. If there is stuff stuck to the center that's another way to tell. Hope some if any of this helps.

 

sounds like a t-stat and heater core for sure.

may need a new radiator cap as well...they should be replaced every few years anyway and it's a cheap enough part to toss on there..

my cap makes a big mess if I try taking it off after running the truck hard.

any coolant smell in the cab will likely be a bad heater core...also poor heat and poor fan speed inside the cab is likely caused by low air flow due to a clogged up evap core.

this is what my evap core looked like when I went in there to replace the heater core:

 

Wow that's dirty. I'll have to look at my t stat and water pump first before I tear into the dash. Thanks for the info guys!

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If you have a leaky heater core that could prevent your cooling system from building pressure. If you don't know the last time the thermostat was changed, just replace it. They will go bad its only a matter of time and they don't cost much. Be sure to get a Cummins thermostat and not a crappy parts store one. I agree with jigabop on the radiator cap, cheap enough to just get one, although yours might not be bad cause your leak in the heatercore could be bleeding the pressure off.

 

I did a little test today. Water pump looked new inside. Tight with no shaft play. Thermostat had made in Germany on it. I boiled it in water. It started to open at 180ish. But only opened 1/4 in. I boiled water to 210 and it stayed 1/4 in. Open. Is this normal? I figured it would open more. Also what is the stock rad cap pressure? Mine says 15lbs

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15-16psi is fine.

 

OK on the psi. Any input on how much a t-stat opens. Mine only opens 1/4inch

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